He may get tired of it. He may get stressed out. Can you switch the lighting around? Move the tank? Put some plants in the tank or around the tank to cut the reflection? Attach a sheet of paper to the side of the tank that's the worst so there is no reflection---create a background.

My betta used to do the same thing. Now he's in a bigger tank with a friend, some fake plants, and a backround on the outside of the tank. He still catches a glimps of himself from time to time, but he's much happier.